1. Field of the Invention
This invention relates to a universal battery charger capable of charging batteries with different voltages.
2. Description of the Related Art
Among various types of battery chargers, universal battery chargers that can charge batteries consisting of different number of cells, i.e., batteries with different voltages, are becoming more common. A universal battery charger can charge, for example, 9.6V, 12V and 14V batteries consisting of 8, 10 and 12 cells connected in series respectively wherein each cell is 1.2V.
The voltage output from the universal battery charger is subject to constant voltage control and the battery charger is set to output a voltage required to charge the batteries consisting of the largest number of cells that the battery charger can handle. This creates a problem in charging batteries consisting of cells fewer in number than maximum. As a result, a large rush current flows in the battery when a switch circuit is closed. This may inflict significant damage on the switch circuit in the charging loop.
When the battery is unloaded from the battery charger or when charging the battery is halted upon detection of the fully charged condition, the switch circuit is turned off so as not to allow the charging current to flow in the battery charging loop. Because a power supply circuit of the battery charger is controlled to output a voltage corresponding to the battery with the largest number of cells, power consumption is larger than necessary.